The present invention relates to an endoscope, and more particularly, to an improvement in the bending mechanism located at the operating portion of the endoscope and which is used for bending a bendable portion of the endoscope.
In general, an endoscope comprises a bendable portion which is located at the front end of an inserting portion and an operating portion which is located at the rear end of the insertable portion in such a manner that the bendable portion can be remotely operated to bend as required by operating the operating portion. Specifically, a sprocket is provided in the operating portion which cooperates with an operating knob to engage a roller chain. Each opposite end of the roller chain is connected to one end of a pair of operating wires which in turn are connected through the inside of the insertable portion to the bendable portion. Accordingly, when the sprocket is rotated with the operating knob, one of the operating wires is pulled by the roller chain and the other operating wire loosens, to permit the bendable portion to be bent in one direction.
With the above construction when one of the operating wires loosens due to the rotation of the operation knob, it tends to move in a zigzag course or get into a peculiar bent shape if the looseness is not removed. When the bendable portion is operated repeatedly in such condition, there is a possibility of the operating wire being cut. Therefore, it is necessary to remove looseness of the operating wire.
In prior art devices, to remove looseness of the operating wire, an inserting passage is formed within the operating portion along the roller chain and a looseness accommodation portion is provided in a part of the inserting passage which is wider in the transverse direction than the remainder of the inserting passage so that the roller chain can be bent within the accommodation portion when the operating wire loosens. Using such a technique, however, where the roller chain is bent within the accommodation portion, it still may happen that link plates of the roller chain located at opposite end positions of the accommodation portion, in the longitudinal direction, are brought into a state where the link plates fall into corners of the accommodation portion. Namely, this happens when the length of the bent portion of the roller chain becomes substantially equal to the length of the accommodation portion in the longitudinal direction. In such a case, even when the operating wire is pushed and pulled, the part of the roller chain fallen in the accommodation portion stops moving. As a result, the bendable portion cannot be restored to its straight condition and the inserting portion may not be pulled out from a coeliac cavity without causing a serious accident.